1. Technical Field
The present invention relates to a reference voltage generator circuit, particularly a reference voltage generator circuit including a band gap circuit.
2. Related Art
A band gap circuit has been used widely various kinds of semiconductor circuits. The band gap circuit is capable of generating voltage with extremely small temperature reliance by taking advantage of a difference in voltage-current characteristics created when two diodes different in size are coupled.
However, the band gap circuit essentially has two stable output voltage points, namely, a normal operating point and a stopping point. If the output voltage becomes stabilized at the stopping point, it is possible that the band gap circuit does not start.
On this account, there is a band gap-based reference voltage generator circuit having a startup circuit so as to bring the output voltage back to one at the normal operating point. The startup circuit is a circuit that brings the output voltage of the band gap circuit back to the normal operating point by forcefully supplying a starting current to the band gap circuit in order to prevent the output voltage from reaching to the stopping point (e.g., see M. Waltari, K. Halonen, “Reference Voltage Driver for Low-Voltage CMOS A/D Converters,” Proceedings of ICECS 2000, Vol. 1, pp. 28–31, 2000).
FIG. 4 shows an example of a conventional band gap-based reference voltage generator circuit. As shown in FIG. 4, the band gap-based reference voltage generator circuit is a band gap circuit 101 with a startup circuit 102 added thereto. The startup circuit 102 monitors an output voltage OUT at an output terminal of the band gap circuit 101, and, when the output voltage OUT is the voltage at the normal operating point, a transistor 111 turns on while transistors 112 and 113 stay off. In contrast, when the output voltage OUT is at the stopping point, the transistor 111 turns off while the transistors 112 and 113 turn on, and, as a result, transistors 114 and 115 turn on, and, thereby, a predetermined current Ia is supplied to a line 116. With the supply of the predetermined current Ia to the line 116, the output voltage OUT rises and reaches to the normal operating point.
As described, the conventional startup circuit 102 brings back the output voltage OUT from the stopping point to the normal operating point by supplying the current Ia in an amount necessary for the startup to the band gap circuit 101. However, even after the band gap-based reference voltage generator circuit has started, a current Ib keeps flowing to a transistor 117 which is coupled in series with the transistor 111 of the startup circuit 102. It is not desirable that the current Ib continue to flow to the transistor 117 even after the band gap-based reference voltage generator circuit has started when considering reducing electric consumption.
In view of these issues, the present invention aims to provide a reference voltage generator circuit which enables to reduce electric consumption.